# What Is “rotational Motion”?

**Rotational motion is motion around an object’s center of mass where every point in the body moves in a circle around the axis of rotation.** The center of mass is the point in an object from which there is an equal amount of mass in any two opposite directions. The axis of rotation is a line that passes through the center of mass.

When an object rotates, the amount a given point moves is not just defined by the distance it travels. It also travels through an angle, the portion of a circle the point transcribes as it rotates. If an object rotates 90 degrees, all the points in an object, save those on the axis of rotation, transcribe a quarter of a circle. The speed at which the points in a rotating object transcribe a circle is known as angular velocity, and a change in that speed is known as angular acceleration.

Rotation is achieved by applying sufficient force anywhere on an object except toward the center of mass. This force is known as torque. A rotating object has inertia just as any object moving a distance does, but this inertia is complex and is determined not just by the total mass of the object but also the relative distance of the mass from the axis of rotation.